The invention relates to hoisting and lifting apparatus and, in particular, to hoisting shackles which will particularly cooperate with special anchoring elements arranged in the load itself. Such hoisting operations are used in connection with prefabricated building elements in the construction industry involving, typically, pre-cast, pre-stressed, post-tensioned and/or reinforced concrete components.
Modern construction technology not only requires the transportation, hoisting and positioning of particularly heavy building components but, as well, requires that such material handling operations be efficient, safe and reduce the probability of damage to the components themselves.
One proposed solution to the above problem is that of incorporating non-recoverable anchoring elements within the building components themselves during fabrication and, thereafter, to attach these components directly to the crane or shackle means. However, one difficulty with the use of such anchoring elements is that such anchoring elements generally form otherwise permanent protrusions from the building component and, thereby, require their removal by cutting, using a blowtorch, or the like.
In order to avoid the above problem, it has been suggested that the anchoring elements be recessed within the pre-fabricated building component such that they would not project over the surface of the component and, therefore, could be left in place after emplacement of the component has occurred. Further, where necessary, the recesses surrounding the anchoring elements could easily be filled in order to thereby remove any trace of the existence of the anchoring elements.
As can be appreciated, it is necessary to accurately position the anchoring elements during the concrete pouring of the building component in order to attain a desired engagement with such anchors by whatever hoisting or lifting means is to be utilized. Thus, it is known in the art to form recesses within building components utilizing an addition to the basic component mold so that a recess will be formed about the anchoring element during the molding process. In this technique, once the concrete and the mold is set, the so-called recess element can be removed from the prefabricated component.
While in many cases the use of recessed anchoring elements offers a certain economy of cost, it has also been the experience of the industry that such recesses may themselves represent a structural problem in that they are either too small for convenient access by conventional hooks or, in some situations, are so large that they may cause structural stress problems by reducing the overall bending resistance of the building component itself.
Several patents in the prior art address the above problems; these patents include: U.S. Pat. Nos. 3,883,170 and 4,173,856 to Fricker; U.S. Pat. Nos. 4,173,367 and 4,296,909 to Haeussler; and U.S. Pat. No. 4,262,951 to Hoyer. Pertinent foreign art includes West German Pat. No. 1,756,603 and West German Published Application No. 27-08-788.
The most pertinent areas of classification are believed to be U.S. Class 294, Sub-Classes 83 and 89.
The invention may be viewed as an effort to provide a more effective shackle, hoisting and positioning means for use in, and in association with, recessed anchoring elements.